For example, in many computer systems, an access from a user program or the like to a secondary storage is performed through a plurality of abstraction and virtualization layers by software and hardware. With these abstraction and virtualization, convenience of an access to a volume of the secondary storage is enhanced. Typical abstraction and virtual layers are a file system and a logical volume provided by an OS.
The file system provides abstract means such as input and output to/from a file, which makes it unnecessary for the user program to directly manage the information about data storage locations in a volume of the secondary storage (for example, to specify a disk block number, the number of blocks, and others).
Also, the logical volume is a virtual volume newly defined from a set of one or more physical volumes (volume group). The logical volume allows abstraction of a volume to be used as a file system and management of the virtual storage separated from the physical volume.
Using a logical volume allows flexible volume management in a computer system. For example, in a logical volume, a plurality of disk devices can be unified and used as a single volume. Conversely, one large volume can be used as a plurality of small volumes. Also, if no space is available in a file system, a physical volume can be added to a volume group to increase the capacity of the logical volume. A file system is constructed on one or more logical volumes created in the above-described manner.
Note that the above-described physical volume is a volume that is physical when viewed from a host. In a storage system typified by a disk array system, by unifying and managing actual physical storage devices in its inside, those storage devices are shown as logical storage devices without showing the internal physical configuration to the host side. Therefore, in the following, physical volumes shown on the host side are referred to as logical storage units (hereinafter referred to as LUs).
On the other hand, as shown in “IPStor® SOLUTION OVERVIEW” issued by FalconStor Japan, 2004 (Non-patent document 1) and “Data Sheet EMC DiskXtender UNIX(registered trademark)/Linux”, EMC corporation (Non-patent document 2), there are some products in which storage devices of different types and different vendors are bundled into one storage device pool and provided as a volume of an arbitrary size or a Network Attached Storage (NAS). These products also include a control technology in which a host defines the secondary storages with different processing speeds and different storage capacities by hierarchy as storage spaces of virtual storage devices, and depending on the frequency of access from the host, data is migrated to storage devices with relatively high processing speed and those with relatively low processing speed.
Furthermore, Japanese Patent Laid-Open Publication No. 9-274544 (Patent document 1) discloses a system in which a plurality of LUs with different processing speeds and different storage capacities are configured in a storage system typified by a disk array system used in connection with a computer. This patent document 1 discloses a technology for the storage system in which the frequency of access from the computer to data stored in the storage devices is managed as statistical information, and based on this statistical information, an LU having a high frequency of access is moved (migrated) to a physical storage device of higher performance.
“Hitachi Freedom Storage (registered trademark) Lightning 9900 (registered trademark) V Series Performance Monitor (Performance Management) User's Guide,” issued by Hitachi Data Systems Corporation, 2002 (Non-patent document 3) discloses a method in which configuration information and statistical information in a disk array system is extracted via a service processor connected to the disk array system. “Hitachi Freedom Storage (registered trademark) Lightning 9900 (registered trademark) V Series Hitachi CruiseControl (registered trademark) User's Guide,” issued by Hitachi Data Systems Corporation, 2002 (Non-patent document 4) discloses an interface using a technology in which an LU having a high frequency of access is migrated to a physical storage device of higher performance based on the statistical information.
“Hitachi Freedom Storage (registered trademark) Lightning 9900 (registered trademark) V Series ShadowImage User's Guide,” issued by Hitachi Data Systems Corporation, 2002 (Non-patent document 5) discloses an interface using a technology in which a copy of an LU is created in a disk array system or among disk array systems.